The ECs earned in chapter 1 will be available until the end of the event.
I don't have any of the Mulan characters, Elastigirl and Frozone around level 5-6 (got them from previous TC), but my LS characters are level 8 and higher.
My storyline characters are at higher levels too for chapter 1.
So, for me, if I were to spend gems, it would be better to do so on current chapter 1 than on next chapters
But it seems TC is getting more expensive each time. I was able to get Jack Jack, CR and The Mayor, but I'm not sure I can get Crikee this time